Although most patients are male, a few heterozygous females have been described with clinical symptoms consistent with MCT8 deficiency resulting from chromosomal translocations and non-random X-inactivation; these individuals often have milder symptoms and less severe thyroid hormone test abnormalities (1, 5, 15, 34). Here, SLC16A2 is linked to hyperinsulinemic hypoglycemia, familial, 4.